The present invention relates to an earth anchor and a method of setting same. More particularly this invention concerns such an anchor provided with externally extending anchor elements serving to hold the anchor firmly in the ground.
An earth anchor is known which is provided with a plurality of laterally displaceable anchor elements which can be extended outwardly through holes in the side of a tube constituting the main body of the anchor. These elements are displaced laterally outwardly after the anchor tube has been driven into the ground. To this end the lower end of the tube is provided with a point facilitating its driving into the ground and the upper end is set up so as to allow mechanism or a tool to be operated that causes these anchor elements to project laterally from the tube after the tube has been driven into the ground. Normally the anchor elements are longitudinally spaced along the tube and extend radially from the tube in different directions.
In a common such arrangement the tube is provided with a plurality of longitudinally spaced and longitudinally extending slots that lie along a helix around the tube. Pivoted at the upper end of each of these slots is a claw which can be pushed outwardly from the interior of the tube so as to engage in the material in which the anchor is being embedded. To this end a tool is inserted into the open top end of the tube and pushed downwardly toward the point, sequently deflecting the claws upwardly and outwardly into the ground.
Such an arrangement has several disadvantages. First of all the pivot arrangement necessary for each of the claws considerably increases the overall cost of the earth anchor. The claws also must be kept relatively narrow, as if they are made too broad the corresponding slots in the tube will greatly weaken the anchor. Thus, the holding power of these claws in the ground is relatively limited. Finally, the pivoting motion of the claws forms an empty space below each claw once it is fully extended, as the claw swings upwardly compressing the earth it passes through upwardly. Since the claws are invariably actuated sequentially from the top toward the bottom the pivoting-up of these claws will tend to pull the entire tube downwardly in the ground, pulling the uppermost claws away from the earth they have compacted. Thus, the arrangement is not securely anchored in the ground.
It has been suggested to avoid some of these disadvantages by forming the anchor elements as pins extendable generally perpendicularly to the tube and mounted at their inner ends on plates pivoted in the tube about respective axes perpendicular to the tube axis. These plates are pivoted in order to extend the pins by means of a lazy-tongs linkage provided with a pair of oppositely threaded nuts operated by means of a screw passing longitudinally through the center of the tube. Such an arrangement is very expensive to produce. Furthermore the relatively narrow anchor elements provide only a limited purchase in the ground so that the holding power of such an anchor is limited. Since a plurality of such pins can be mounted on a single swingable flap, the lowermost pins are, indeed, longer than the upper pins. Nonetheless due to their limited effective surface area this increased length hardly increases the holding power.
Prior-art earth anchors can be seen in German Pat. Nos. 231,278 and 234,455.